1. Field of Invention
The present invention relates to a method of manufacturing a thermal bubble inkjet print head and the structure for the same. More particularly, the invention relates to a manufacturing method of a monolithic integrated thermal bubble inkjet print head and the structure for the same.
2. Related Art
In the conventional thermal bubble inkjet print head structure, the print heads developed by, for example, Hewlett Packard (the U.S. Pat. Nos. 4,490,728 and 4,809,428), Canon (the U.S. Pat. Nos. 4,596,994 and 4,723,129) or Xerox (the U.S. Pat. Nos. 4,774,530 and 4,863,560) are the side shooting ones as shown in FIGS. 1A and 1B and the roof shooting ones as shown in FIGS. 2A and 2B. FIG. 1B is a cross-sectional view of FIG. 1A in the A-Axe2x80x2 direction, and FIG. 2B is a cross-sectional view of FIG. 2A in the B-Bxe2x80x2 direction. The basic structure of these two types of thermal bubble inkjet print heads contains: an ink channels 1, a nozzle 2 for releasing ink, an orifice plate 3, an energy transducer 10 for converting electrical energy into thermal energy, and protection layers 7, 8 formed above and below the energy transducer 10. The ink channel 1, the nozzle 2, and the orifice plate 3 are all formed on a substrate 4. The energy transducer 10 can be composed of a thermal resistor film 5 and wires 6 in a proper layout. The function principle of the thermal bubble print head is to use the resistor heated energy transducer 10 to heat up the ink in the ink channel 1 and jet out the ink. When printing, the inkjet print head receives a current pulse provided by the printer. The current pulse is transmitted through the wire 6 to the energy transducer 10. Therefore, the energy transducer 10 generates a short high temperature to vaporize the ink. The ink vapor rapidly expands to provide a pressure to jet out the ink droplet from the nozzle 2.
Most of the conventional manufacturing methods for thermal bubble inkjet print head grow a heat insulation layer on a silicon chip, such as SiO2, and then deposit thermal resistant materials and conducting materials by sputtering. Afterwards, the standard integrated circuit manufacturing technologies, such as masking, exposure, developing, and etching, are employed to form an electricity-heat energy transducer and connection wires. Later on, other protection layers and ink channels formed with dry films are provided. Finally, an orifice plate is attached to form an inkjet element. Another conventional method, proposed by Xerox, is to make the ink channels on another silicon chip (different from that with the thin film thermal resistor) and then combine both chips by bonding. However, the above-mentioned conventional method has to separate the inkjet print head into several different pieces and then assemble then together. For example, the chip with the thermal resistor, the orifice plate, and the materials for forming the ink channels are separately made and will be combined together through precision alignment and bonding. Thus, the conventional methods inevitably require high manufacturing costs.
To solve the above defects, Eastman Kodax proposed in the U.S. Pat. Nos. 5,463,411 and 5,760,804 that an anisotropic etched (110) silicon chip can be used to form an ink channel, wherein the micro-channel goes through the whole chip from the chip back. Although this method can be used in forming a monolithic integrated inkjet print head structure, it has to use metal foil on the chip back to make a throttle slit for preventing ink back flows. Furthermore, the method will form bubbles on the micro-channel wall surfaces while anisotropic etching. Therefore, the stability and yield of such manufacturing processes are hard to control.
Therefore, there is a need to develop a new manufacturing method and a structure of a new thermal bubble inkjet print head that can solve the above-mentioned problems.
It is thus an object of the invention provide a manufacturing method and a structure of a monolithic integrated inkjet print head that only require a simple manufacturing process and lower costs.
Pursuant to the above object, the present invention uses semiconductor manufacturing technologies to configure all elements in a thermal bubble inkjet print head. For example, an ink channels, an ink slot, an energy transducer, and an orifice plate are all finished on the same substrate. This method for making thermal bubble inkjet print heads is particular useful in all batch processes and does not need the step of precision alignment and bonding for orifice plates in conventional methods. Therefore, the present invention can greatly increase the production efficiency and lower the manufacturing costs.
According to the disclosed method, each part in the structure of the inkjet print head is finished on the same substrate. The top side of the substrate has a top surface and the back side has a back surface. The method comprises the following steps: (a) forming a patternized sacrifice layer on the top surface to define an ink channel pattern; (b) forming a first protection layer on the top surface and the sacrifice layer, forming a second protection layer on the back surface, and making a mesh on the first protection layer of the sacrifice layer; (c) etching the sacrifice layer and the top surface of the substrate using the anisotropic etching technology to form the ink channels; (d) forming a planarizing insulation layer on the first protection layer to fill the mesh; (e)forming energy transducers and proper wires corresponding to the ink channels on the planarizing insulation layer; (f) forming an insulation layer on the wires and the energy transducer to protect the wires and the energy transducer; (g) etching at least one ink slot connecting to the ink channels on the back of the substrate; (h) etching proper electrical pads and orifices connecting to the ink channels on the top surface of the substrate; and (i) forming an orifice plate on the top surface of the substrate.
The monolithic integrated inkjet print head structure manufactured according to the above method is not limited by the low resolution of the dry film materials and the electroforming nozzle plate in the prior art. It can further minimize the ink channels and the orifice so as to decrease the volume of ink droplet being jetted out. This helps increase the orifice density and dot per inch (DPI) resolution. The structure is easier to be expanded into a page-wide print head.
Moreover, in the monolithic integrated print head structure, the ink slots and the energy transducers are installed on different surfaces of the substrate and, the transducers and the orifices doesn""t need to at the same positions. This helps in the circuit layout for increasing the orifice density.